This invention relates generally to the field of vehicle seating where seat components must be made as efficiently as possible, preferably with easily recyclable materials, and be resistant to permanent deformation. This invention uses a novel process to form a body of thermoplastic polymeric fibers and improve resistance of the body to permanent deformation.
Presently, most vehicle seat bodies are made of polyurethane foam. While satisfactory results have been achieved with polyurethane foam, many advantages accompany the use of thermoplastic polymeric fibers. Vehicle seat bodies made of thermoplastic polymeric fibers are more breathable, can achieve equivalent support in a lower profile and lighter weight body, and can be formed and laminated with a fabric cover in a very simple and efficient process. It is also possible to employ the same polymeric material for both the thermoplastic fibers of the body and a fabric cover, so that no separating is necessary before recycling.
These advantages are achieved by covering at least some of the polymeric fibers with a fusable polymeric coating that melts and forms bonds when activated by heat. Polymeric fibers are placed in a mold cavity having the shape of the desired vehicle seat component. The polymeric fibers are then compressed and a heated atmosphere is passed through the cavity, causing the polymeric coating to melt and flow over adjacent fibers, forming bonds as it cools.
However, bodies made of thermoplastic polymeric fibers are susceptible to permanent deformation under certain conditions. If a heavy object, such as a tool box, is left on the body at elevated temperatures, a permanent mark may be left in the body in the shape of the object. This type of deformation can occur during the initial loading at an elevated temperature and to a lesser degree during subsequent loadings.
Under normal conditions, the bonds between polymeric fibers cause the body to bounce back to its original shape after being subjected to a load. However, when the temperature is elevated beyond the glass transition temperature, the weight of the object causes the weaker bonds to break and the polymeric fibers plastically deform or creep. The body no longer completely rebounds to its original shape.
The glass transition temperature is actually a finite temperature range over which the polymer retains an amorphous, liquid-like structure, but at temperatures below the glass transition temperature the molecular motion becomes frozen and the material turns into a glass. These qualities are displayed at a temperature below the melting point of the material. The precise glass transition temperature for a material will depend on molecular weight, the rate of cooling and other factors.
A principal object of this invention is to reduce the occurrence of permanent deformation of vehicle seat components made from thermoplastic polymeric fibers. To this aim, the body is compressed during formation with a second, heavier load while above the glass transition temperature, but below the melting temperature of the fusable polymeric coating. The weaker bonds between fibers will break and the fibers will deform or creep during this compression step. Stronger bonds will be formed in the desired shape.